International observers have cited numerous violations in Sunday's parliamentary elections in Russia.

The OSCE said the polls were slanted in favour of pro-Kremlin party United Russia, noting apparent manipulations such as the stuffing of ballot boxes.

But President Dmitry Medvedev said the vote was fair, honest and democratic.

On Monday night, at least 2,000 people protested in central Moscow against PM Vladimir Putin, and demanded honest elections.

The election saw a sharp drop in support for United Russia, ahead of Mr Putin's bid to return to the presidency next March.

With nearly all the votes counted, electoral officials said the party had just under 50%, down from 64% in 2007.

United Russia lost 77 seats, in a vote which is being seen as a popularity test for Mr Putin.

'Like a game'

Reading a communique, an official from the Organisation for Security and Co-operation in Europe (OSCE) said the election had in general been "well organised" but there were severe problems with the counting process.

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Media captionPetros Efthymiou, OSCE: "The contest was slanted in favour of the ruling party"

"The contest was also slanted in favour of the ruling party, the election administration lacked independence, most media were partial and state authorities interfered unduly at different levels," said Petros Efthymiou.

Another observer, Heidi Tagliavini, said the elections had suffered because several opposition parties were barred from taking part.

"To me, this election was like a game in which only some players are allowed to compete," she said.

The OSCE report prompted US Secretary of State Hillary Clinton to express "serious concerns" about the conduct of the election.

Analysis

By Daniel SandfordBBC News, Moscow

Vladimir Putin is facing a slump in popularity that he has not experienced since the Kursk submarine disaster of 2000.

There are still many in Russia who do not blame him for the rampant corruption and the stagnant economy.

But he is the leader of United Russia, and support for the party has fallen significantly in these Duma elections, which inevitably reflects badly on him.